Multilayer Functional Tapes Cofired at 450 °C: Beyond HTCC and LTCC Technologies

Traditional ceramic device fabrication relies on high-temperature processes that increase energy costs and limit material compatibility. Prior research has shown that high-temperature cofired ceramic (HTCC) and low-temperature cofired ceramic (LTCC) technologies remain the standard for multilayer ceramic substrates. However, these methods still require elevated temperatures that may degrade sensitive components. No prior work had resolved the challenge of fabricating functional ceramic substrates at significantly lower temperatures while maintaining electrical performance. This gap motivated the search for alternative materials and fabrication methods that could reduce energy consumption and expand design possibilities. The need for ultralow-temperature cofiring has remained unmet in the field of ceramic electronics. Researchers have explored various composite systems, but none have achieved stable, functional substrates at 450 °C. This paper addresses that limitation by introducing a novel composite system suitable for cofiring with silver electrodes at this low temperature.

The goal of this study was to develop a ceramic composite suitable for cofiring at ultralow temperatures. The researchers aimed to create a multifunctional substrate that could support device fabrication while maintaining electrical and mechanical stability. They focused on a lead zirconium titanate (PZ29)-glass composite, which could be processed at 450 °C without degrading performance. The team sought to evaluate the feasibility of tape casting, lamination, and sintering at this low temperature. They also aimed to assess the surface roughness of the green and sintered tapes to determine suitability for device-level fabrication. The study aimed to measure key electrical properties, including dielectric permittivity, loss, and thermal expansion. The researchers intended to compare their results with existing HTCC and LTCC technologies to highlight advantages. Their ultimate goal was to establish a new fabrication strategy for low-cost functional ceramic devices.

The team used a commercial PZ29-glass composite as the base material for tape casting. They formulated a novel slurry composition suitable for low-temperature cofiring with silver electrodes. The tapes were cast using a standard tape casting process and then isostatically laminated to form multilayer structures. The lamination process ensured uniform thickness and alignment of the layers. The green tapes were sintered at 450 °C to produce the final substrate. Surface roughness was measured for both green and sintered tapes using profilometry techniques. Ferroelectric and piezoelectric properties were evaluated using standard electrical testing methods. Dielectric permittivity and loss were measured at 2.4 GHz using impedance analysis. Thermal expansion was assessed over a temperature range of 100-300 °C. The long-term stability of the tape was monitored over 28 months to evaluate shelf life.

The sintered substrate achieved a surface roughness of 355 nm, suitable for device-level postprocessing. The composite showed a piezoelectric coefficient (d₃₃) of 17 pC/N and a voltage coefficient (g₃₃) of 30 mV/N. Dielectric permittivity was measured at 57.8 with a low loss of 0.05 at 2.4 GHz. The relative permittivity varied by 23% over the temperature range of -40 to 80 °C. The thermal expansion coefficient averaged 6.9 ppm/°C between 100 and 300 °C. The tape remained stable over 28 months, with no significant degradation of dielectric properties. The surface roughness of the green tape was 146 nm, indicating compatibility with standard fabrication techniques. These results suggest that the material is suitable for ultralow-temperature cofiring with silver electrodes.

The authors propose that their PZ29-glass composite enables cofiring at 450 °C with commercial silver electrodes. They suggest that the surface roughness of the sintered substrate supports device-level fabrication. The dielectric properties indicate compatibility with high-frequency applications. The thermal expansion coefficient suggests dimensional stability over a wide temperature range. The long-term stability of the tape over 28 months supports its practicality for industrial use. The low sintering temperature reduces energy costs compared to HTCC and LTCC technologies. The researchers suggest that this method opens new possibilities for low-cost ceramic device fabrication. They propose that this approach could lead to broader adoption of ultralow-temperature cofiring in the electronics industry.